"Fat Boy" 12/118 thrust engine

[Deleted]

Hi John

Hope you and the family had a good time over the holidays

Glad to see things going back together, looking forward to seeing what results the change of turbine wheel brings

Happy new year

All The best
Andy

[racket]

Hi Guys

Engine back together and mounted on the test stand .

New 130/112mm turb wheel fitted ( Thanks Monty) into a new jetpipe/exducer shroud , jetpipe is made from a section of 5" OD exhaust pipe









I want to do some static testing of the starter motor now to see what difference there is to achievable RPM without any "fuel" being added, hopefully the greater exducer deflection with increased power addition from the turb wheel will help the starter to achieve higher RPM.

Cheers
John

[finiteparts]

John,

It's looking good...can't wait to see it running.

Good luck!

Chris

[racket]

Hi Chris

Yep , things are looking up :-)

Just finished some starter testings which were encouraging .

My test this morning with "stale" batteries , they've been sitting for a month since their last charge and had ~12.6 volts in each of them, yet produced 12,800 rpm on the first "spoolup" and 12,200rpm on the second one with 72 psi oil pressure and 25 C oil temp .

After recharging to 13.8 and 13.7 volts I achieved 13,000 and 12,400 from the two tests , only a couple of hundred rpm more than the morning tests ,so the batteries must have been reasonably OK in the morning .

I performed some RPM tests ~13 months ago and was only able to produce ~10,800 rpm with the previous turb wheel and "big" pipe .

Thats only a couple of thousand rpm difference but if we check the difference in "tip speeds squared" , its ~45% improvement , 340 ft/sec vs 282 ft/sec tip speeds .

I can't wait to give her a test run with some fuel to help the spoolup, hopefully I won't be needing the previous 30,000 rpm to get her "over the hump" , previous engines only needed a bit over 20,000 ,LOL.... I'll be up to that with only a bit of propane preheat :-)

Cheers
John

[turboron]

John, good progress. Looking forward to the first run.

Thanks, Ron

[monty]

I can't wait to see this thing run!!

Monty

[stoffe64]

Good luck my friend on your next spoolup
Cheers/Stephan
Once again thanks Monty!!

[racket]

Hi Guys

Whilst waiting for more favourable weather conditions to do a test run I've been trawling through some of the turbo Forums for any info on G Trim turb wheels (~112mm exducer) and it appears they're capable of flowing ~100 lbs/min Corrected Flow , this sorta corresponds with the flow map I have for the TV91 F Trim wheel ( ~106 mm exducer) which has 90 lbs/min with a "largish" 1.70 A/R scroll, the smaller 1.46 A/R flows 85 lbs/min Corrected at a 2:1 PR, then both flat line after that.

The extra 6 mm of exducer diameter on the G Trim will provide another ~10% flow area .

After doing more calcs using the 100 lbs/min number it looks like I might have to run the engine up to a bit higher PR if I want to squeeze my 3.6 lbs/sec through.

Cheers
John

[CH3NO2]

Hi John,

Your description of running at higher pressure ratio to squeeze the flow through the turbine sounds a lot like what I was working on this week. 

I ran the numbers on a 85mm GTX5533R turbo to see if its compressor could push its flow through its turbine and came up with this plot.  Turbine choked flow rate  Vs P.R. overlaid on the compressor flow Vs P.R.  The compressor and turbine match up at a pressure ratio of 1.5 and 4.0.

Is this the same kind of matchup or crossover you are referring to? 





The compressor line is the line of maximum compressor efficiency.

Thanks,
Tony

[racket]

Hi Tony

Yep , the higher PR, "lowers" the Corrected Flow back to what the map allows.

I might eventually have to "adjust" the NGV throat area , its probably a tad too large at present , I'll see how the next test run goes and whether or not theres sufficient extra gas deflection to power up to higher rpm without excessive temps , the smaller exducer flow area might pull back the mass flow to a point where NGV velocities are too low, reducing gas deflection at the turb wheel inlet , negating the benefits of the new exducers "extra" deflection............its a matter of getting the balance right .

Cheers
John

[azwood]

I bet your itching for a test run I haven't run the kart in a while due to bush fire season

[azwood]

Been in search of a decent needle valve for the throttle they all seem to need like five turns to open them do you have any idea where to get something userble with a throttle wheel jhon.

[racket]

Hi Aaron

Yeh , the bushfire season has been a bit of a bummer this year , now we've got high winds as well , by next week theres supposedly easterly winds with showers so maybe OK if I can dodge them .

On my bike I used a needle valve with a throttle cable arrangement in place of the handle , this was only possible because of the "pressure differential valve" in the system which provided a constant pressure drop across the throttle irrespective of supply pressure/flow , by adjusting the size/diameter of the throttle cable disc on the valve handle I was able to produce a "sweet" throttle at the handlebar .

On my karts I used more of a carburetor needle type arrangement that closed off an oriface to reduce the dump back to tank to increase fuel flow to the engine .

Cheers
John

[CH3NO2]

Feb 22, 2019 19:56:05 GMT -5 racket said:

Hi Tony

Yep , the higher PR, "lowers" the Corrected Flow back to what the map allows.

I might eventually have to "adjust" the NGV throat area , its probably a tad too large at present , I'll see how the next test run goes and whether or not theres sufficient extra gas deflection to power up to higher rpm without excessive temps , the smaller exducer flow area might pull back the mass flow to a point where NGV velocities are too low, reducing gas deflection at the turb wheel inlet , negating the benefits of the new exducers "extra" deflection............its a matter of getting the balance right .

Cheers
John

Hi John,

Yeah, thats what I recently discovered. A higher PR can lower the corrected flow.
PR Vs Corrected flow
C=m_dot*sqrt(T_01/T_a))/(p_01/p_a)

71.3

80.2

81.3

78.5

73.4

69.5

64.2

59.9


This was done in comparison to the published flow chart of 70 lbs/min.   It was confusing seeing the results for the first time.   Flow going up then down?  Initially it was assumed the flow would only increase with increasing PR, but after thinking about it some more it became apparent why.  It's not actual flow, its "corrected" flow.

BTW I thought you were changing out the turbine to increase its flow. Is the root problem a lack of turbine power or a lack of turbine flow? 

Thanks,
Tony

[racket]

Hi Tony

The larger G Trim wheel has less flow area out of the exducer than the highly clipped F Trim wheel its replaced , but because of the extra gas deflection I won't need as much expansion velocity to get more gas deflection , so hopefully the gases can be more dense exiting the exducer compensating for the smaller flow area ,the extra deflection might provide enough power for higher rpm without exceeding max temps , the higher PR will also compensate for the smaller flow area ...........its a fine line I'm treading :-)

Depending on how the compressor efficiency behaves itself with any change in flow/PR I might need more or less power per pound of air which will then influence whats required across the turb stage , I don't have the luxury of much buffer zone if I want to maximise mass flow potential...............the easy way out would be to "tighten" up the NGV throats/angles to get more gas deflection going in, but at the price of mass flow reduction, ......that combined with the extra deflection from the G Trim wheel would result in an easy engine to "tune" ...................but power output would be reduced considerably , I might as well have just built another engine with a smaller inducered comp wheel .............this was always going to be "challenging" , buts thats exactly what I wanted/needed , its forcing me to think and come up with solutions by trying different things .

Cheer
John